We will study neurons in the cat's visual cortex that respond preferentially to elongated stimuli presented at a particular position and angular orientation upon the retina to determine: 1) the development of their orientation-specificity, 2) the short term and the long term susceptibility of this selective response to modification by sensory stimulation, 3) the effects of sensory input upon the distribution of orientation preferences of cortical cells, 4) the effects of visual experience on the distribution throughout the visual cortex of the X-cell and of the Y-cell afferents to these cells, and 5) the function of orientation-sensitive cells. Both conventional acute electrophysiological recording techniques and chronically implanted arrays of recording microelectrodes will be used to study the development of the orientation-sensitivity of cells in the visual cortex of kittens. Using animals that receive controlled early visual experience, we hope to discover whether stimulation: 1) facilitates or maintains pre-existing preferences, 2) modifies pre-existing preferences, or 3) induces orientation-selectivity in cells previously non-selective. The visual capabilities of normal cats and of cats reared in restricted visual environments will be measured by a series of behavioral tests and these capabilities related to the response properties of cells in the visual cortex of these animals.